A．there was an increase in the human consumption of salt
B．salt -eaters have bad health conditions
C．the environment was strictly monitored
D．high -blood pressure was easier put under control

A．because members of the same family tend to use similar amounts of salt
B．to explore the long - term use of a sodium - based substance
C．because it was proved that salt caused high blood pressure
D．because of the availability of chemically pure salt and its derivatives